1. Field of the Invention
The present invention relates to a process for the suspension polymerization of vinyl chloride, either alone or in admixture with other monomers.
2. Description of the Prior Art
It is known that, in the suspension polymerization of vinyl chloride, either alone or in admixture with other monomers, remarkable amounts of polymer accumulate onto the walls of the autoclave. The importance of such a deposit is normally depending on the type of stirring, on the formulations which are used (type and amount of suspending agents and of catalysts), on the impurities present in the monomers and on the number of polymerization runs carried out.
Such a deposit reduces the heat transmission through the walls of the autoclave and gives place to difficulties in controlling the reaction; moreover the product is highly contaminated by hard and vitreous crystals. As a rule the scales are removed, after each polymerization run, either manually and with high pressure water, which is anyhow requiring one hour or longer times; moreover, in the case of manual operation, problems of environment hygiene arise for the personnel attending to the descaling operation. The Italian Pat. No. 874,456 in the name of B. F. Goodrich Co., relates to a process for the suspension polymerization of vinyl chloride, according to which the aforementioned drawbacks are mitigated due to the addition, during the reaction, of magnesium hydroxide, at the maximum proportion of 1000 ppm referred to the monomers.
Thus, an essential reduction of the incrustations is obtained, as well as a simultaneous worsening of the porosity and of the heat stability of the polymer: the addition of magnesium hydroxide in an amount higher than 1000 ppm causes an intolerable deterioration of the product.